Over 90 million Americans (greater than 40 percent) will seek medical attention for dizziness or some other balance disorder sometime in their life. A NIH working committee recently reported that at least 2 million Americans experience chronic impairment due to dizziness or other balance disorders, causing medical expenses in excess of 1 billion dollars per year. Many of these chronically impaired patients could benefit from vestibular rehabilitation, and some of these patients could benefit from a vestibular prosthesis (similar to the cochlear implant for profound sensorineural hearing loss). This proposal directly addresses both of these health care needs. Specifically, the proposed studies develop and test a prototype neural prosthesis. Furthermore, to enhance our understanding of vestibular adaptation, the proposed studies use this prototype device to investigate adaptation to changes in peripheral vestibular stimulation. This study will be the first to comprehensively investigate adaptation to changes in chronic, peripheral stimulation of the vestibular system. A better understanding of vestibular adaptation will lead to improved vestibular rehabilitation. These general scientific goals will be achieved by investigating the following specific aims: 1. Study the importance of bilateral versus unilateral cues. 2. Study how the nervous system adapts to changes in peripheral stimulation of the branch of the vestibular (VIIIth) nerve that innervates the lateral semicircular canal. 3. Study how the nervous system combines sensory information from the otolith organs and semicircular canals when the rotational cues are provided via electrical stimulation. 4. Study how the nervous system adapts to yaw rotational cues delivered to a nerve branch innervating one of the vertical canals that does not normally include yaw rotational information. 5. Study how the nervous system adapts to constant-rate electrical stimulation while stationary, with and without visual cues. All of these proposed specific aims will be investigated by measuring changes in the vestibulo-ocular responses induced by changes in chronic, patterned, electrical stimulation of the peripheral vestibular system.